In the U.S., air pollution in general worsened markedly across the country between 2015 and 2017, probably due to rising temperatures, according to the American Lung Association’s State of the Air 2019 report. Based on federal, state and local data, it found that that many cities nationwide increased the number of days when particle pollution, often called “soot”, soared to record-breaking levels. More cities suffered from higher numbers of days when ground-level ozone, also known as “smog”, reached unhealthy levels. The report’s three-year span covered the hottest years on record globally, and as the report noted, the data “adds to the evidence that a changing climate is making it harder to protect human health.” Case in point: The top six cities or metro areas in ozone pollution—Los Angeles-Long Beach, Visalia, Bakersfield, Fresno-Madera-Hanford, Sacramento-Roseville and San Diego-Chula Vista-Carlsbad—were all located in California, one of the most environmentally proactive states.